On PHPMaster.com there's a tutorial posted for those out there already using MongoDB for their architecture and might be looking for administration tools. In this recent postAshish Trivedi looks at one offering, RockMongo (a PHP-based tool), and some of the features it provides.

There are many such GUI tools available, like Rockmongo, PHPMoAdmin, Fang of Mango, UMongo, MongoExplorer, and MongoVUE, to name just a few. When it comes to using MongoDB with PHP-based projects, Rockmongo and PHPMoAdmin are good options. In this article, we’ll take a look at Rockmongo. Rockmongo is an open source MongoDB administration tool written in PHP5. You’ll become familiar with using Rockmongo to create databases, collections and documents, query collections, and import and export data.

The download and install are pretty simple and he includes a screenshot of what you should see when it's all set up. There's also several other screenshots included showing how to do things like create databases, insert documents, use "explain" and importing/exporting databases.